Properties anisotropic adhesives

The electrical properties and the reliability of connections made of an anisotropic adhesive loaded with both deformable conductive particles and non-deformable dielectric particles used as spacers have been reported [108]. The amount of deformation of the conductive particles is calculated from their diameter, 10 xm, relative to the diameter of the spacers, 4, 6, 8, and 10 p,m. Plotting the electrical resistance of the connection as a function of the number of particles, the authors show that the resistance decreases when the particle count expands from 5 to 60... 

Anisotropic adhesives are more sensitive than isotropic conductive pastes to the coplanarity of the connecting pads and leads of the substrate and the device because many of them are based on the single-particle bridging concept. The typical properties of a screen-printable isotropic conductive adhesive paste are a silver content of 70-75% by weight, a viscosity of about 80 Pa s, and a curing time of 15 s at 175°C. This fast cure cycle produces an adhesive layer with Tg... 

Plywood panels consist of several large thin wood veneer-type layers joined with adhesive. Some or all of the layers are sheets of veneer. Other layers, particularly in the core, may be particleboard, hardboard, lumber strips, and special materials. The fiber direction of each layer is at right angles to that of the adjoining layer. This cross-banding makes plywood more uniform and less anisotropic than lumber its properties in the direction of panel length resemble those in the direction of panel width. 

Anisotropic Material property with behavior differing in dependence on stress direction, for example, wood, electrical properties of special conductive adhesives opposite isotropic. 

Isotropic (Iso (Greek) = same tropos (Greek) = direction) Same properties of a substance in all directions (e.g., electric properties of special conductive adhesives) Opposite anisotropic. 

The properties of a two-phase system consisting of a continuous "matrix" phase and a discontinuous "filler" phase are calculated in tenns of the component properties and volume fractions. It is assumed that the thennoelastic properties within each phase domain are homogeneous and isotropic, and that there is perfect adhesion between adjacent phase domains. The shapes of the filler particles are assumed to have biaxial symmetry. If a filler particle is anisotropic (as in fibers or platelets), it is oriented uniaxially at this stage of the calculation. Particle shape is described by the aspect ratio Af (defined as the ratio of the largest dimension of the filler divided by its smallest dimension), and if Af l then also by... 

Table 6.5 Properties of anisotropic conductive film adhesives" ...

Materials for use as anisotropically conductive adhesives must satisfy requirements even more stringent than those defined previously for isotropically conductive adhesives. No specifications, however, have been defined specifically for these materials. When used for flip-chip applications, the adhesive not only serves as a physical and electrical interconnection between the device and the substrate, but also serves as the environmental protection and passivation layer. This fact, combined with high adhesive concentrations, makes the ionic contamination levels of these materials more critical than for isotropic conductive adhesives. In addition, the processing of these materials has a greater influence on joint reliability as the anisotropic electrical properties develop only after heat and pressure are applied to the joint. 

In the case of rigid plastics, the greatest problems are in reinforced plastics, which are often anisotropic, having directional strength properties. Joints made from such substrates should be designed to stress both the adhesive and the adherend in the direction of greatest strength. Laminates should be stressed parallel to the laminations to prevent delamination of the substrate. ... 

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